1. FIELD OF THE INVENTION
This invention pertains to flow devices such as valves and switches activated by differential fluid pressure. For example, this invention may be used as an excess fluid flow check valve, or a switch actuator to close an electrical circuit responsive to fluid flow.
2. DESCRIPTION OF RELATED ART
In most cases present fluid flow devices such as check valves are spring loaded toward open positions and when differential pressure exceeds a predetermined value the valves close.
However, there are certain disadvantages to the utilization of spring biased valves, and in particular spring biased poppet-type check valves. A spring exerts increasing force against the flow as the poppet is closing and, thus, the closing action is less positive and less reproducible.
Further, exact reproduction of spring performance is difficult and expensive. Therefore, it is difficult and expensive to make excess flow check valves with repeatably accurate closing pressure. This is especially true for low flow (low differential pressure) excess flow check valves.
Still further, poppet valves and associated springs are relatively heavy and are adversely affected by gravity when differently oriented relative to the direction of gravity forces, especially under low pressure differential operating conditions.